1. Field of Invention
The invention relates to a film scanner and to a method for the optical scanning of a motion picture film.
2. Description of Prior Art
A film scanner of this type serves for the scanning of the image information of an exposed film, for example for the purpose of digital post-processing. A transmission arrangement is usually provided for this purpose, with the film material to be scanned being illuminated on the one side and an optical receiving system and a light receiver being arranged on the other side.
The motion picture film is transmitted intermittingly in such a film scanner to sequentially illuminate the individual exposed image sections, i.e. the individual image sections following one another, and to scan them optically. It is desired in this process to scan a sequence of mutually following individual image sections without any image shift, in particular without any horizontal image shift (weave) and without any vertical image shift (jitter). The image sections should therefore be detected in an unchanging relative position with respect to the film track and with respect to the visual field of the light receiver of the film scanner in order to avoid “jolts” on a later playback of the scanned image sequence.
It is known for this purpose, for example for a motion picture film of the type 35 mm, to fix the position of the motion picture film precisely in a position of rest between two transport movements, with usually locking register pins engaging into the perforation holes which are provided on both longitudinal sides of the film and serve for the transport of the film by means of a sprocket drum. A mechanical registration of this type, however, results in unwanted wear of the perforation holes. Aged footage 5 can have shrunk or be very brittle so that it can be damaged on the introduction of the registration pins into the perforation holes. Cut points and paste points can additionally prevent the mechanical registration with the aid of the locking register pins from working with the desired precision.
A further disadvantage in film scanners having intermittent film transport and mechanical registration is a lower speed in comparison with film scanners having continuous film transport since the film transport, the mechanical registration and the scanning have to take place after one another. This has the result that only approximately 8 to 10 images per second can be scanned so that the duration of the scanning procedure increases approximately threefold with respect to the original running speed of the film.
It is known to detect the actual image position using capacitive or optical methods and to carry out a corresponding post-positioning of the image or a subsequent image steadiness correction. DE 10 2005 042 136 A1 thus discloses a film scanner which has, in addition to the light receiver for the generation of the scanned images, a separate image sensor which only scans the perforation holes. Such an arrangement is, however, undesirably complex from a construction aspect. In addition, on the use of additional sensors, there is the need to adjust them relative to the main image sensor.